Red Mountain

Prospect, Active

Commodities and mineralogy

Main commodities Pt
Other commodities Au; Cr
Ore minerals chromite; gold; platinum group metal alloys

Geographic location

Quadrangle map, 1:250,000-scale HG
Quadrangle map, 1:63,360-scale D-6
Latitude 58.94
Longitude -161.73
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is on the east side of Red Mountain on the ridge between Boulder and Squirrel Creek drainages. The map site is at the approximate center of a large soil geochemistry anomaly at an elevation of about 1,000 feet. It is accurately located.

Geologic setting

Geologic description

Red Mountain is a large, composite ultramafic pluton of Jurassic age (Hoare and Coonrad, 1978). It is dominantly dunite with a thin border zone assemblage of peridotite, clinopyroxenite, and hornblende-bearing rocks (Southwith, 1986; Southwith and Foley, 1986; Alaska Earth Sciences, 2000). This prospect is in dunite between the crest of Red Mountain and the eastern border zone of the pluton. It is defined by a soil-geochemistry anomaly that is 1,700 meters (5,600 feet) long and 700 meters (2,300 feet) wide. Platinum values in this anomaly range from 60 to 3,300 ppb (Alaska Earth Sciences, 2000). Bird and Clark (1976, Table 4, p. 724) reported Red Mountain sample results of up to 1.4 ppm Pt, 0.020 ppm Pd, 0.0300 ppm Rh, and 0.300 ppm Ir. Fechner (1988, p. 43) reported Red Mountain sample results of up to 1.681 ppm Pt, 0.515 ppm Pd, 0.117 ppm Rh, and 0.823 ppm Ir.
Chromite occurs as disseminations and layers in the dunite. Platinum-bearing alloys have been identified as inclusions in chromite (Bird and Clark, 1976) and as separate grains in heavy mineral concentrate from residual materials over dunite (Fechner, 1988). Three samples of heavy-mineral concentrate contained a trace to 0.0011 ounce of PGM per cubic yard and a trace to 0.0002 ounce of gold per cubic yard. Platinum was recovered from concentrates of residual materials over dunite sampled near the crest of Red Mountain by the Goodnews Bay Mining Company in 1965 (Mertie, 1969, p. 84). The platinum-bearing alloy inclusions in chromite comprise 20 percent platinum, 40 percent iridium, 25 percent iron and lesser amounts of rhodium, nickel, and chromium (Bird and Clark, 1976, p. 724).
Geologic map unit (-161.7322264802, 58.9392161759122)
Mineral deposit model Alaskan PGE (Cox and Singer, 1986; model 9).
Mineral deposit model number 9
Age of mineralization Jurassic, the age of the Red Mountain ultramafic pluton. Hoare and Coonrad (1978) report K/Ar ages for two samples of amphibole from the southeast border of the Red Mountain pluton: 176.4 +/- 5.3 Ma and 186.9 +/- 5.6 Ma.
Alteration of deposit Partial to complete serpentinization of the dunite is common. Mertie (1969, p. 79) reports that 25 percent of the Red Mountain dunite is serpentine.

Production and reserves

Workings or exploration A surface soil and rock geochemical survey has been completed over a large part of the Red Mountain dunite. An aeromagnetic survey was flown over the Salmon River (Goodnews) area in 1994, a gravity survey has been completed, and some controlled-source audio magneto-telluric lines have been run over selected parts of the ultramafic complex (Alaska Earth Sciences, 2000). A portable washing plant was used for trial placer prospecting of residual material on the crest of Red Mountain in 1965.
Indication of production None

Additional comments

The Red Mountain dunite is probably the major source of platinum metals in the placer deposits of the Salmon River drainage.

References